System and method for reticle protection and transport

ABSTRACT

A substrate protection and transport system and method for transitioning a substrate from atmospheric pressure to vacuum in a lithography tool. The system includes one or more removable substrate transport cassettes that support a substrate. The cassette can include a base portion and top portion, and can include a seal. Each cassette has at least one vent and at least one filter. The system further includes a box having a base and lid. The box holds one or more cassette-substrate arrangements. A storage rack having shelves for holding the box-cassette-substrate arrangement is also provided. Further, an entry-exit module having a loadlock is provided for transitioning the cassette-substrate arrangement from atmospheric pressure to vacuum. The entry-exit module can include a shuttle and/or elevator for transporting the cassette-substrate arrangement. During transitioning, the filter(s) and vent(s) restrict particles within the loadlock from entering the cassette-substrate arrangement and reaching a surface of the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/216,660, filed Aug. 12, 2002 (now pending), which is acontinuation-in-part of U.S. patent application Ser. No. 09/925,722,filed Aug. 10, 2001 (now U.S. Pat. No. 6,619,903 B2, issued Sep. 16,2003), both of which are incorporated herein by reference in theirentireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to lithography, and more specificallyto the protection of lithographic reticles.

2. Related Art

Lithography is a process used to create features on the surface oftargets. Such targets can include substrates used in the manufacture offlat panel displays, circuit boards, various integrated circuits, andthe like. A semiconductor wafer, for example, can be used as a substrateto fabricate an integrated circuit.

During lithography, a reticle, which is another exemplary substrate, isused to transfer a desired pattern onto the desired target. The reticleis formed of a material transparent to the lithographic wavelength beingused. For example, in the case of visible light, the reticle would beformed of glass. The reticle has an image printed on it. The size of thereticle is chosen for the specific system in which it is used. Duringlithography, a wafer, which is supported by a wafer stage, is exposed toan image projected onto the surface of the wafer corresponding to theimage printed on the reticle.

The projected image produces changes in the characteristics of a layer,for example photoresist, deposited on the surface of the wafer. Thesechanges correspond to the features projected onto the wafer duringexposure. After exposure, the layer can be etched to produce a patternedlayer. The pattern corresponds to those features projected onto thewafer during exposure. This patterned layer is then used to removeexposed portions of underlying structural layers within the wafer, suchas conductive, semiconductive, or insulative layers. This process isthen repeated, together with other steps, until the desired featureshave been formed on the surface of the wafer. As should be clear fromthe above discussion, the accurate location and size of featuresproduced through lithography is directly related to the precision andaccuracy of the image projected onto the wafer.

In addition to the transmissive reticles just described, reflectivereticles are also used in the art. For example, reflective reticles areused for short wavelength light that would otherwise be absorbed by atransmissive glass reticle.

In an effort to keep contamination of the reticle surface to a minimum,lithography processing is performed in a “clean room.” A clean room isan enclosure having a specified controlled particle concentration. Inorder to maintain the specified controlled particle concentration,gaseous materials are provided to and removed from the enclosure. Aconsiderable amount of expense is associated with maintaining a cleanroom. This expense is related, in part, to the size of the clean roomand the equipment needed to maintain it. For example, as reticles aretransported from one stage in a lithographic process to another, theyare susceptible to contamination due to particles found within theprocessing area. To minimize the potential for contamination, the entireroom in which the reticle is transported is usually maintained in aclean state. Thus, there is an incentive to reduce the environment thatmust be maintained in the clean state. A further incentive for reducingthe size of the clean room is safety. In some cases, clean rooms areoxygen deficient and therefore unfit for human occupancy. If the cleanroom can be isolated to a smaller environment, then the surrounding areacan be maintained for safe use and occupancy by humans.

In general, reticles arrive to and leave from lithography tools,including EUV lithography tools, in a closed box or “pod”. Vibration,pressure shock, and turbulent air flow can result from opening the boxand may stir up particles that are initially resting on the internalsurfaces of the box, such as the top-side of the base or the inner wallsand ceiling of the lid. Particles can become detached from the surfacesand then move freely and randomly within the gas volume inside the box.Some particles can eventually re-deposit on the exposed surfaces of anunprotected reticle within the box.

U.S. Pat. No. 6,239,863 (incorporated by reference herein in itsentirety), issued to Catey et al., May 29, 2001, and commonly assignedto Silicon Valley Group, Inc., now ASML US, Inc., discloses a removablecover for protecting a reticle used in a lithography system. Theremovable cover includes a frame and a membrane supported by the frame.The removable cover can further include at least one reticle fastenerthat applies force to the reticle, thereby preventing movement of theremovable cover relative to the reticle when the removable cover is inplace. However, the use of the reticle fastener presents an opportunityfor contamination from the contact between the reticle and the reticlefastener.

Reticles are typically stored in an atmospheric environment. Inpreparation for exposure, the reticles are transported from theatmospheric environment to a high vacuum environment. Of prime concernin EUV lithography, is how to transition reticles from the atmosphericpressure environment to the high vacuum environment without addingparticles to critical areas of the reticle henceforth, the “reticlepattern” or the “patterned areas” during transient confusion. Transientconfusion refers to the stirring up of the particles in the loadlock ofthe EUV lithography tool by the turbulent air currents resulting fromhaving to remove the air from the loadlock. This is a new problem in thecontext of lithography tools, since the EUV tool is the first tool toexpose the reticle in vacuum and without a protective pellicle.

A similar problem has been encountered before by those who design thetools that write masks, henceforth “mask writer tools”. Mask writertools use one or more electron beams to write mask blanks directly fromthe design data, a few pixels at a time, which takes a long time (asopposed to copying a pattern from the mask to the wafer in one quickpass with light as lithography tools do). Electron beams in mask writershave always required the reticle to be exposed in high vacuum and haveprecluded the use of pellicles, similarly to EUV light in lithography.

In the paper titled “New Mask Blank Handling System for the AdvancedElectron Beam Writer” (published in the proceedings of the 19th AnnualBACUS Symposium on Photomask Technology, September 1999, SPIE Vol. 3873,ref # 0277-786×/99) Yoshitake et al. describe their solution to theproblem. In summary, Yoshitake found that if during the transitionbetween atmospheric pressure and vacuum, the mask blank is maintainedinside a box having membrane filters (the Clean Filter Pod or CFP), manyfewer particles tend to settle on the mask blank. Hence, Yoshitake'ssolution was to put the mask blank inside a permeable-to-gas-only box,place the box inside the loadlock, transition the loadlock betweenatmospheric pressure and vacuum, open the box, and remove the mask blankfrom the box and the loadlock.

The Yoshitake solution, however, introduces additional problems to besolved. First, in the example where the masks are contained in a closedbox or pod, the masks are unprotected. Consequently, there is apotential for contamination of the masks when the closed box or pod isopened. Second, in the example where the masks are contained in a boxhaving filters, the same device is used to remove the mask blanks fromthe box. This creates the potential for cross-contamination.

Briefly stated, there is a need for a way of further reducing thepotential for reticle contamination during transport. Likewise, there isalso a need to reduce the potential for reticle contamination while itis transitioning between atmospheric pressure and vacuum.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a substrate protection and transportsystem and method for transitioning a substrate from atmosphericpressure to vacuum in a lithography tool. The system includes one ormore removable substrate transport cassettes that support a substrate,forming one or more cassette-substrate arrangements. In an embodiment,the removable substrate transport cassette includes a base portion and atop portion, and can also include a seal. Each cassette can also includean edge band that can provide a surface to support the top portion ofthe removable substrate transport cassette. Each cassette has at leastone vent and at least one filter. The system further includes a boxhaving a base and a lid. The box holds one or more of thecassette-substrate arrangements, forming a box-cassette-substratearrangement. A storage rack having shelves for holding thebox-cassette-substrate arrangement is also provided. Further, anentry-exit module having a loadlock is provided for transitioning thecassette-substrate arrangement from atmospheric pressure to vacuum. Theentry-exit module can include an atmospheric de-podder to detach the boxbase from the box lid. The entry-exit module can also include a shuttlefor transporting the cassette-substrate arrangement, and can furtherinclude an elevator. During transitioning, the filter(s) and vent(s)restrict particles within the loadlock from entering thecassette-substrate arrangement and reaching a surface of the substrate.

The method for transitioning a substrate from atmospheric pressure tovacuum includes loading the substrate into a removable substratetransport cassette to produce a cassette-substrate arrangement andloading the cassette-substrate arrangement into a box to produce abox-cassette-substrate arrangement. The method also includestransporting the box-cassette-substrate arrangement to a shelf of afirst storage rack and transporting the box-cassette-substratearrangement out of vacuum from the first storage rack to an entry-exitmodule. The method further includes unlatching a lid of the box from abase of the box and lowering the base on an elevator, the basesupporting the cassette-substrate arrangement. The method also includesengaging the cassette-substrate arrangement with a shuttle, using theshuttle to transport the cassette-substrate arrangement into a loadlock,an transitioning the loadlock from atmospheric pressure to vacuum. Atleast one vent and at least one filter of the cassette-substratearrangement restrict particles within the loadlock from entering thecassette-substrate arrangement and reaching a surface of the substrate.

These and other advantages and features will become readily apparent inview of the following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The present invention is described with reference to the accompanyingdrawings. In the drawings, like reference numbers indicate identical orfunctionally similar elements. Additionally, the left-most digit of areference number identifies the drawing in which the reference numberfirst appears.

FIG. 1 is an illustration of a reticle transport system in accordancewith an embodiment of the present invention.

FIG. 2 is an illustration of a removable reticle cassette according toan embodiment of the present invention.

FIG. 3 is an illustration of an arrangement of a reticle and pelliclewithin a removable reticle cassette according to an embodiment of thepresent invention.

FIGS. 4 and 5 are illustrations of a method of loading a reticle into aremovable reticle cassette according to an embodiment of the presentinvention.

FIG. 6 is an illustration of a substrate transport system in accordancewith an embodiment of the present invention.

FIGS. 7A-7H, show simplified side views of an embodiment of a substratetransport system and other portions of a lithography tool in accordancewith an embodiment of the present invention.

FIG. 8 is an illustration of a removable substrate transport cassetteaccording to an embodiment of the present invention.

FIGS. 9A-9K show simplified side views of an embodiment of a substratetransport system and other portions of the lithography tool inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be discussed in detail.While specific features, configurations and arrangements are discussed,it should be understood that this is done for illustration purposesonly. A person skilled in the relevant art will recognize that othersteps, configurations and arrangements or devices may be used to achievethe features of the invention without departing from the spirit andscope thereof. Indeed, for the sake of brevity, conventionalelectronics, manufacturing of semiconductor devices, and otherfunctional aspects of the method/apparatus (and components of theindividual operating components of the apparatus) may not be describedin detail herein.

FIG. 1 illustrates a reticle transport system 100 for a lithographytool. The reticle transport system 100 includes an indexer 105. Inaccordance with an embodiment of the present invention, the indexer 105further comprises a library of shelves (not shown) within thelithography tool. An inert gas atmosphere is maintained within theindexer 105. According to an embodiment, for example, the indexer 105 isfilled with nitrogen gas and other gaseous materials necessary to meetthe clean room requirements.

A plurality of reticles 109 are stored on shelves (not shown) within theindexer 105. Reticles are used to transfer a particular pattern onto asubstrate such as a semiconductor wafer, a panel display, a circuitboard, and the like. The reticle can be of the reflective ortransmissive type, as would be apparent to a person skilled in thelithography art. To protect the reticle 109 from contamination, apellicle 110 may be fixed over the reticle 109. An example of a pelliclethat can be used in connection with the present invention is describedin commonly owned, co-pending U.S. non-provisional patent applicationSer. No. 09/501,180, filed Feb. 10, 2000 (now U.S. Pat. No. 6,507,390B1, issued Jan. 14, 2003), titled “Method and Apparatus for a Reticlewith Purged Pellicle-to-Reticle Gap,” which is incorporated herein byreference.

Although the reticles in FIG. 1 are positioned vertically to each other,this presentation is for example only and not limitation. In alternativeembodiments, the reticles could also be stored horizontally to oneanother. Likewise, in another embodiment, the reticles could be storedon a carousel and the reticles rotated to a particular position withinthe indexer. In an embodiment, the reticle 109 and pellicle 110 arestored upside down. In this way, any contaminants falling on the reticlewill be on the backside. If the reticle 109 and pellicle 110 are storedupright (as depicted in FIG. 1) then the end effector 113 could be madeto rotate the reticle and pellicle upside down. After reading thisdisclosure, a person skilled in the relevant art(s) will recognize otherarrangements for storing reticles 109 and pellicles 110 within theindexer 105, without departing from the scope of the present invention.

A removable reticle cassette 111 is also stored within the indexer 105.The removable reticle cassette 111 is used to house the reticle 109during transport. The environment of the removable reticle cassette 111is also maintained in a “clean” state. In this way, the clean room stateis maintained in a much smaller volume of space. Although the indexer105 is shown containing only one removable reticle cassette 111, this isfor example only, and is not intended to limit the present invention.The number of removable reticle cassettes 111 and likewise, the numberof stored reticles 109 are determined by the space constraints of theindexer 105. The present invention is described with reference to areticle, having a pellicle attached thereto. However, this is forexample only, and not limitation. Reticles, without a pellicle, can beused without departing from the scope and spirit of the presentinvention. Further details of the removable reticle cassette 111 will beprovided below with respect to FIG. 2.

The reticle transport system 100 further comprises an end effector 113,coupled to a robotic arm 115. The end effector 113 engages one of theplurality of reticles 109 and pellicle 110 in order to position thereticle 109 and pellicle 110 within the removable reticle cassette 111.In alternative embodiments, a wand or other manual or robotic devicecapable of engaging the reticle or pellicle (if present) may also beused. In an embodiment, the end effector 113 engages the reticle 109 andpellicle 110 through electrostatic attraction. In alternativeembodiments, the end effector 113 could engage the reticle 109 andpellicle 110 through vacuum attraction.

A seal 117 is also used in the reticle transport system 100. The seal117 is used to secure the reticle within the removable reticle cassette111. The seal 117 can be any device capable of securing the reticle 109within the removable reticle cassette 111 while at the same time,preventing contaminants from entering into the removable reticlecassette and nitrogen from escaping the removable reticle cassette 111.For example, the seal 117 could be a vacuum seal or a magnetic seal.Accordingly, a vacuum system, a magnetic system, or the like, can alsobe used in connection with the present invention to facilitate thesealing function.

The reticle transport system 100 further comprises a door 107. The door107 is used to keep the contaminants from coming into the indexer 105and the nitrogen gas from seeping out. In alternative embodiments,indexer 105 may be provided with more than one door 107. For example,additional doors may be used to provide access to the indexer 105 formanual or automatic loading of the plurality of reticles 109 and theremovable reticle cassette 111. Foreseeable reasons for accessing theindexer 105 might also include repair of the indexer 105, replacement ofthe reticles 109, or the like. Still further, the end effector 113 couldbe made to pass through one or more doors 107 before engaging thereticle 109.

FIG. 2 provides a perspective view of an exemplary removable reticlecassette 111 in accordance with an embodiment of the present invention.In this embodiment, the removable reticle cassette 111 comprises aninner chamber 205 and an outer chamber 210. The inner chamber 205carries the reticle 109 and the pellicle 110. The inner chamber 205 issealed within the outer chamber 210 by the seal 117 during reticleexchanges. The outer chamber 210 is used to contain the nitrogen gas andother gaseous materials necessary to provide the clean stateenvironment.

The material used for the removable reticle cassette 111 should becompatible with standard cleaning agents used with lithography systems.The materials should not result in the production of outgassing ofamines, or other undesirable substances harmful to the lithographicprocess. Still further, the material should be resistant to mechanicaldegradation. Examples of possible materials that could be used includefiber reinforced molded polymers, Derlin (trademark) or PTFE (Teflon(trademark)) coated metals such as aluminum or titanium. Other materialsmay be used without departing from the scope of the present invention.

In accordance with embodiments of the present invention, the removablereticle cassette 111 accommodates reticles with any type of pellicle andreticles without a pellicle. Furthermore, the removable reticle cassette111 also accommodates solid or breathable pellicle frames.

FIG. 3 provides an illustration of the arrangement of a reticle 109 andpellicle 110 sealed within the removable reticle cassette 111, which isready for transport by the robot arm 115, in accordance with anembodiment of the present invention. The end effector 113 is shownengaging a reticle and pellicle. In alternative embodiments, a wand orother mechanical, electromechanical, or robotic device capable ofengaging the reticle or pellicle may also be used. After reading thisdisclosure, additional engaging means will be apparent to a personskilled in the relevant art(s). A method for transporting a reticle 109from the indexer 105 will now be described with respect to FIGS. 4 and5.

Referring to FIG. 4, a method of transporting a reticle 109 from theindexer 105 in a lithography system begins with the opening of the door107 to allow the end effector 113 to gain access to the contents of theindexer 105.

Next, the reticle 109 and pellicle 110 are engaged by the end effector113. In accordance with embodiments of the present invention, the endeffector 113 can engage the reticle 109 and pellicle 110 by means of avacuum, electrostatic charge, magnet, wand, or other lifting devices.Once the reticle 109 and pellicle 110 are fixed to the end effector 113,the robot arm 115 is used to maneuver the end effector 113 toward theremovable reticle cassette 111. In an embodiment, the reticle 109 andpellicle 110 would be oriented so that they are upside down. In thisway, any potential contamination would be on the backside of thereticle.

FIG. 5 depicts the reticle 109 and pellicle 110 being loaded into theremovable reticle cassette 111, such that the removable reticle cassette111 does not come into contact with the reticle 109 and pellicle 110.Once the reticle 109 and pellicle 110 are placed within the removablereticle cassette 111, the seal 117 is used to secure the cleanenvironment, thereby producing a sealed arrangement.

Finally, the robot arm 115 is used to transport the sealed arrangementfrom the indexer 105 to a mount for performing lithographic exposure.Once the lithographic exposure process is completed, in accordance withembodiments of the present invention, the sealed arrangement is returnedto the indexer 105. The reticle 109 and pellicle 110 are then removedfrom the removable reticle cassette 111 through reversal of the processdescribed in FIGS. 4 and 5.

As mentioned above, how to transition reticles from an atmosphericpressure environment to a high vacuum environment, without addingparticles to critical areas of the reticle, is of prime concern in EUVlithography. Accordingly, exemplary systems and methods for a substratetransport system for use in transitioning reticles in an EUV lithographytool in accordance with embodiments of the present invention will now bedescribed.

The term substrate is used in some of the exemplary embodimentsdescribed herein. In other exemplary embodiments reference is made to areticle. It will be apparent to persons of ordinary skill in the artafter, reading the disclosures herein, that substrates other thanreticles, for example, mask blanks, wafers, flat panel displays, and thelike can be used. Such equivalent substrates are considered to be withinthe scope of the present invention.

An exemplary substrate transport system 699 will now be described withreference to FIGS. 6 and 7A-7H. An exploded view of removable substratetransport cassette 600 comprising shell 607 is shown in FIG. 6. In anembodiment, substrate 601 fits horizontally in tray 603. The four bottomcorners of the substrate 601 engage tray locators 605. Tray 603 andsubstrate 601 fit inside shell 607 through opening 611. Opposite end 624of shell 607 is a closed end. With tray 603 positioned inside shell 607,flange 609 seals opening 611 with a latching means (not shown),substantially preventing the flow of gas and particles through saidopening. Latching means can comprise, for example, permanent magnets,electromagnets, mechanical latches, passive hooks and eyes, and thelike. Additional means for sealing flange 609 to opening 611 would beapparent to persons skilled in the relevant arts based on the teachingsdescribed herein. The arrangement of the substrate 601 within theremovable substrate transport cassette 600 is referred to herein as acassette-substrate arrangement.

In an embodiment, shell 607 is further provided with one or more filters621 and vents 626. Preferably, gas, but not particles, can flow throughfilters 621 and vents 626. In an embodiment, one filter 621 and vent 626is located opposite to a patterned side 623 of the substrate 601. InFIG. 6, consistently with actual orientation in an EUV tool, thepatterned side 623 faces downward towards tray 603. Therefore a blankside 625 of the substrate 601 faces upwards, towards filter 621 and vent626. Even though the filters and vents do not allow through flow ofparticles, contaminant particles, which may initially be attached to theinner side of the filters 621, may become dislodged when gas flows fromthe exterior to the interior of the removable substrate transportcassette 600 during a pressure transition (i.e. venting). Due to theorientation of the substrate 601, the dislodged particles are morelikely to impinge on substrate's 601 blank side 625 than on itspatterned side 623. Thus, by favorably locating at least one filter 621relative to the patterned side of the substrate 601, the pattern can bekept more particle-free.

In an embodiment, substrate transport system 699 is further comprised ofa substrate transporter 627. Using an end effector 615, avacuum-compatible manipulator or motion device henceforth “vacuum robot”(not shown), can hold and transfer substrate 601 within substratetransporter 627 from station to station within a lithography tool.Further descriptions of this process are provided below with respect toFIGS. 7A-7H.

Continuing with the present description, the end effector 615 isprovided with at least one end effector locator 619. To facilitateholding of the substrate transporter 627, an engaging tab 613 is coupledto flange 609. The engaging tab is provided with tab locators 617. Inthis way, end effector locators 619 of the end effector 615 canrespectively engage tab locators 617 of engaging tab 613. The endeffector locators 619 and engaging tab locators 617 pairs can comprisepins in holes, pins in slots and the like. When shell 607 is attached toflange 609, vacuum robot can use the end effector 615 and engaging tab613 to move the reticle transporter 627, shell 607, and the enclosedsubstrate 601 from station to station within the process chamber of thelithography tool. Additional embodiments of substrate transport system699 will now be described with reference to FIGS. 7A-7C and 7F-7G.

Referring to FIG. 7A, in an embodiment of the present invention,substrate transport system 699 is further comprised of a box 701. Box701 is used to contain the cassette-substrate arrangement. A populartype of box is the “Standard Mechanical Interface (SMIF) reticle pod”.Henceforth, however, “box” will be used generically to describe anyairtight container having a substantially planar base 711 and adetachable lid 713 in which the substrate 601 is transported frommachine to machine. A handle 715 coupled to lid 713 enables amanipulator or motion device, henceforth “atmospheric robot” 717 to pickup box 701 by handle 715. Latching means (not shown) keep the base 711and the lid 713 temporarily coupled. A seal (not shown) between the base711 and the lid 713 prevents gas and particles from flowing in and outof the box 701.

In an embodiment of the present invention the substrates 601 and theremovable substrate transport cassettes 600 would be stored andtransported inside the box 701. The arrangement of thecassette-substrate arrangement inside the box is referred to herein as abox-cassette-substrate arrangement. Each substrate 601 would be insideits own removable substrate transport cassette 600, which in turn wouldbe inside the box 701. For simplicity and clarity, the descriptionsherein are limited to boxes that hold only one substrate, such assubstrate 601, for example, but it will be immediately apparent thatboxes holding a plurality of substrates can also be handled by thepresent invention. For example one type of SMIF reticle pod presently inuse can hold up to six reticles. In an embodiment of the presentinvention, the box 701 is temporarily placed on a shelf 707 of a firststorage rack 709. In an embodiment, the first storage rack 709 is an“out of vacuum (OOV) rack”.

Referring to FIG. 7B, in accordance with an embodiment of the presentinvention, substrate transport system 699 is further comprised of adetacher 718. Detacher 718 is capable of detaching the base 711 from thelid 713. Exemplary detachers include a “de-podding station”, and amanual SMIF de-podding station, also known as a “pod popper”.

Referring to FIG. 7C, in an embodiment of the present invention, thesubstrate transport system 699 is further comprised of a loadlock 719.The loadlock 719 includes atmospheric-side door 721 and vacuum-side door723, which couples the loadlock 719 to a process chamber 725. Thevacuum-side door 723 is provided to enable a vacuum compatible transfermechanism, henceforth “vacuum robot” 727 access into loadlock 719. Thevacuum robot 727 is able to couple itself to removable substratetransport cassette 600 using locator pairs 617 (not shown) and 619.

Referring to FIG. 7F, in an embodiment of the present invention,substrate transport system 699 is further provided with a second storagerack 731 located within process chamber 725. The second storage rack 731has a plurality of shelves 729 for storing the removable substratecassette 600 and substrate 601 (i.e., cassette-substrate arrangement).An exemplary second storage rack is an in-vacuum (IV) library.

Referring to FIG. 7G, in yet another embodiment of the presentinvention, substrate transport system 699 is further comprised of alocking device 733. The locking device 733 engages a recess (not shown)in shell 607, temporarily coupling shell 607 to second storage rack 731.

An exemplary method for transitioning a substrate, such as substrate601, from atmospheric pressure to vacuum in a lithography tool using asubstrate transport system in accordance with an embodiment of thepresent invention will now be described with reference to FIG. 7A-7H.

Referring to FIG. 7A, upon arriving at the lithography tool, box 701containing a removable substrate transport cassette 600 and substrate601 (box-cassette-substrate arrangement) is temporarily placed on ashelf 707 of a first storage rack 709. Upon receiving a request forbringing a specific substrate, for example, substrate 601, into thevacuum process chamber, atmospheric robot 717 takes thebox-cassette-substrate arrangement from first storage rack 709 andtransports it to a detacher 718 to detach the base from the lid. FIG. 7Bshows base 711 resting on detacher 718. The lid 713 has already beenremoved and is not shown. Robot 717 holds the cassette-substratearrangement.

Vibration, pressure shock, and turbulent air flow resulting from openingthe box 701 may stir up particles that are initially resting on theinternal surfaces of the box 701, such as the top-side of the base orthe inner walls and ceiling of the lid 713. Particles can becomedetached from the surfaces and then move freely and randomly (Brownianmotion) within the gas volume inside the box 701. Some particles caneventually re-deposit on the exposed surfaces of substrates within thebox 701. For example, if the box 701 contains an unprotected reticle,the particles can settle on the exposed surfaces of the reticle.However, because the reticle of the present invention is completelyenclosed and protected by the removable substrate transport cassette600, the particles are impeded from reaching any surfaces of thereticle.

Referring to FIG. 7C, atmospheric robot 717 places thecassette-substrate arrangement inside loadlock 719. During this step,atmospheric-side door 721 remains open, while vacuum-side door 723remains closed. The atmospheric robot 717 then leaves thecassette-substrate arrangement inside the loadlock 719 and withdraws.After the atmospheric robot 717 is withdrawn, atmospheric-side door 721closes and the loadlock 719 is pumped down to vacuum. The pumpdown stepis illustrated in FIG. 7D.

During pumpdown, the substrate 601 undergoes the transition fromatmospheric pressure to vacuum. More particularly, gas is allowed tomove out of the removable substrate transport cassette 600 throughfilter 621 and vent 626, but particles that are outside the removablesubstrate transport cassette 600 are impeded from entering the removablesubstrate transport cassette 600 and contaminating the substrate 601.During pumpdown of the loadlock 719, some of the particles that areresting on the internal surfaces of the loadlock 719 may be stirred upand begin to move freely and randomly within the loadlock 719. Likewise,particles that are resting on the external surfaces of the removablesubstrate transport cassette 600 may also become detached and begin tomove freely and randomly within the loadlock 719. However, none of theparticles are able to reach the substrate 601, because the filter 621and vent 626 along with the solid walls of the removable substratetransport cassette 600 are impenetrable barriers to particles.

It is possible that there are some particles resting on the interiorwalls of the removable substrate transport cassette 600 when thesubstrate 601 is first placed inside the removable substrate transportcassette 600. To minimize the presence of these interior particles, theinterior surfaces of the removable substrate transport cassette 600should be thoroughly cleaned before introducing the substrate 601.However, as would be apparent to one skilled in the relevant arts, it isnearly impossible to eliminate every particle, even with the bestavailable cleaning techniques. Therefore, the possibility of migrationof any remaining interior particles to critical areas of the substrate601 must also be minimized. Accordingly, in embodiments of the presentinvention, the gas flow velocity is reduced, thereby minimizing thetendency of particles to become detached from the interior walls of theremovable substrate transport cassette 600. In an embodiment of thepresent invention, the filter 621 and vent 626 provide means of ensuringa low flow velocity inside the removable substrate transport cassette600, because they slow down the through passage of molecules. It isimportant to have a sufficiently large total filter area for avoidingdamage that may occur to the filter 621 if too much of a pressuredifference is allowed to develop across the thickness of the filter.Such potential for damage is created by excessively restricting thetotal amount of open area available for gas molecules to leave theremovable substrate transport cassette 600. In addition, using a filterthat excessively restricts gas flow requires long pump down times, whichmay decrease the throughput of the lithography tool, resulting inadverse economical impact.

It has been observed that gas flow affects the behavior of particlesresting on surfaces differently, depending on the size of the particles.Larger particles (e.g., >5 microns) tend to become detached easily,while smaller particles (e.g., <0.1 micron) tend to cling tenaciously tosurfaces. The larger the particle, the more likely it is to come off asurface for a given gas flow velocity. Fortunately, for this samereason, larger particles are also easier to clean off from surfaces,which means that they are unlikely to be found inside a thoroughlycleaned removable substrate transport cassette 600. Therefore, in anembodiment of the invention, it is adequate to remove the gas in theremovable substrate transport cassette 600 at a rate (henceforth“maximum allowable gas flow velocity”) just low enough not to dislodgeparticles equal to or smaller than a given size, for example 1 micron,which is somewhat greater than the particle size that can be removedefficiently by the cleaning process, for example 0.5 micron.Statistically in this example, since particles >0.5 micron are unlikelyto be present after cleaning, and since the flow speed is less than whatis likely to disturb particles >1 micron, it is very unlikely that anyremaining particles (<0.5 micron) will become detached from the interiorsurfaces of the removable substrate transport cassette during a pressuretransition. The maximum allowable gas flow velocity should be measuredinside the removable substrate transport cassette at locations near thefilter 621 since velocity increases as one approaches the inlet oroutlet orifice of a container.

An even greater measure of protection can be attained by protectingsensitive areas of the substrate 601 from particles by attaching aremovable cover to the substrate 601. Accordingly, in an embodiment ofthe present invention, a removable cover, such as a pellicle, disclosedin U.S. Pat. No. 6,239,863 (cited above) is attached to the reticle andthe covered reticle is enclosed inside the removable substrate transportcassette 600. Unless otherwise noted, the words “mask” and “reticle”refer both to bare reticles and to reticles protected by a removablecover in the context of the present invention.

Referring to FIG. 7E, after pump-down, vacuum-side door 723 opens andvacuum robot 727 reaches into loadlock 719. After coupling itself to thecassette-substrate arrangement using locator pairs 617 and 619, robot727 removes the cassette-substrate arrangement from loadlock 719 andbrings it into process chamber 725.

Referring to FIG. 7F, vacuum robot 727 places the cassette-substratearrangement on second storage shelf 729 and uncouples itself from thecassette-substrate arrangement. In an embodiment of the presentinvention, substrates remain stored inside their removable substratetransport cassette 600 within the second storage rack library until aspecific substrate, for example, substrate 601 is requested for ejectionfrom the process chamber or a specific substrate, such as substrate 601is requested for lithographic exposure in the vacuum chamber, henceforth“processing”. Where ejection from the chamber is requested, thecassette-substrate arrangement containing the specified reticle isremoved by following the steps described above in exact reverse order.Further steps for processing the substrate 601 in the lithographicexposure stage of the process chamber will now be described withreference to FIGS. 7G and 7H.

Referring to FIG. 7G, as vacuum robot 727 approaches to attach itself tothe cassette-substrate arrangement, locking device 733 deploys, engaginga recess (not shown) in shell 607. In this way, the locking device 733temporarily couples shell 607 to second storage rack 731.

Referring to FIG. 7H, vacuum robot 727 pulls substrate transporter 627containing substrate 601, separating it from shell 607, which remainsempty on shelf 729 of second storage rack 731. Although not shown, fromhere, the vacuum robot 727 places the substrate 601 on the mount orchuck of a stage (not shown). Substrate 601 is then separated fromsubstrate transporter 627. In an embodiment of the present invention,during and after chucking, the substrate transporter 627 remains coupledto the vacuum robot 727. Removal of the substrate 601 from the stage,replacement of the substrate transporter 627 and substrate 601 in theempty shell 607, which remained in the second storage rack 731, andrelease of the locking device 733 follow the above steps in exactreverse order.

An alternative embodiment of a removable substrate transport cassette isillustrated in FIG. 8. Referring to FIG. 8, a removable substratetransport cassette 800 comprising base portion 807 and top portion 811is shown. A substrate 801 having downward-facing patterned area 803(depicted by the dashed X-ed rectangle), rests on the removablesubstrate transport cassette's 800 bottom portion 807. Morespecifically, lower corners 809 of the substrate nest inside baseportion locators 805 of base portion 807. The removable substratetransport cassette's top portion 811, henceforth “top” rests on thesubstrate 801. More specifically, upper corners 813 of the substrate 801fit inside the nest formed by top portion locators 815 in top 811. Withsubstrate 801 nested in the base portion 807 and top 811 resting on thesubstrate, seal 817 interfaces with first surface 819. The purpose ofseal 817 is to prevent particles from entering the removable substratetransport cassette 800. Seal 817 can be permeable to gases but notparticles. For example, in an embodiment, the seal 817 can be a“tortuous path seal”, comprising a raised surface with protrudingconcentric vertical flanges that loosely fit into corresponding groovesin first surface 819. Alternatively, seal 817 can be chosen to beimpermeable to both gases and particles. For example, in an embodiment,seal 817 is an O-ring type elastomer seal, as depicted in FIG. 8. Withtop 811 in place, edge band 821 loosely surrounds the base portion'sside edges 823. The purpose of edge band 821 is to further impede themigration of particles from outside to inside the removable substratetransport cassette 800, by creating a more tortuous path. The edge band821 is further used to provide a second surface 825 that can be used tosupport top 811 when the removable substrate transport cassette 800 isheld in an open state for extracting the substrate 801. A filter 827 andvent 829 are located towards the blank side of the substrate, facingaway from patterned area 803. Filter 827 and vent 829 allow gases tomove freely in and out of the closed removable substrate transportcassette 800, but impede the through flow of particles. A substratetransport system comprising a removable substrate transport cassette 800in accordance with embodiments of the present invention will now bedescribed with reference to FIGS. 9A-9B and 9H-9J.

Referring to FIG. 9A, in an embodiment of the present invention, asubstrate transport system 999 is comprised of a box 903. Box 903 isused to contain removable substrate transport cassette 800 and substrate801. A popular type of box is the “Standard Mechanical Interface (SMIF)reticle pod”. Henceforth, however, “box” will be used generically todescribe any airtight container having a substantially planar base 919and a detachable lid 915 in which the substrate 801 is transported frommachine to machine. A handle 905 coupled to lid 915 enables amanipulator or motion device, henceforth “atmospheric robot” 901 to pickup box 903 by handle 905. Latching means (not shown) keep the base 919and the lid 915 temporarily coupled. A seal (not shown) between the base919 and the lid 915 prevents gas and particles from flowing in and outof the box 903.

In an embodiment of the present invention the substrates 801 and theremovable substrate transport cassettes 800 would be stored andtransported inside the box 903. Each substrate 801 would be inside itsown removable substrate transport cassette 800 (thereby forming acassette-substrate arrangement), which in turn would be inside the box903 (thereby forming a box-cassette-substrate arrangement). Forsimplicity and clarity, the descriptions herein are limited to boxesthat hold only one substrate, but it will be immediately apparent thatboxes holding a plurality of substrates can also be handled by thepresent invention. For example one type of SMIF reticle pod presently inuse can hold up to six reticles.

In an embodiment of the present invention, the box-cassette-substratearrangement is temporarily placed on a shelf 909 of a first storage rack911. In an embodiment, the first storage rack 911 is an “out of vacuum(OOV) rack”.

Referring to FIG. 9B, in an embodiment of the present invention, thesubstrate transport system 999 is further comprised of an entry-exitmodule 913. The entry-exit module 913 is comprised of a detacher (notshown), a loadlock 925, and a transfer shuttle 923. Still further, in anembodiment, entry-exit module 913 is further provided with a ledge 917and an elevator 921. In yet another embodiment, the entry-exit module913 is comprised of an atmospheric-side gate valve 931, a vacuum-sidegate valve 933, and a process chamber 937.

In an embodiment, the compact arrangement of the entry-exit module 913greatly reduces the range of motion required from the atmospheric robot901. In this way, the use of a much smaller atmospheric robot 901 ispossible. The ability to use a smaller atmospheric robot 901 frees upvaluable space, which is generally very scarce in a lithography tool. Inaddition, the use of a smaller atmospheric robot 901 in accordance withan embodiment of the present invention reduces the amount of heat andvibrations generated by the robot 901. Heat and vibrations are majorsources of performance degradation in lithography tools.

As shown in FIG. 9H, in yet another embodiment of the present invention,entry-exit module 913 is further comprised of a vacuum robot 935.

FIG. 9I shows a simplified front view of a second storage rack 939. Inan embodiment of the present invention, the vacuum robot 935 transfersthe cassette-substrate arrangement to the second storage rack 939 whichis located within process chamber 937. The second storage rack 939 isprovided with a plurality of shelves 941 and ledges 943. Furtherfeatures for processing the substrate in a lithographic exposure stageof the process chamber 937 will now be described with reference to FIG.9J.

Referring to FIG. 9J, in preparation for lithographic exposure, vacuumrobot 935 places substrate 901 onto a chuck 945 of a lithographicexposure stage 947. Chuck 945 can be, for example, an electrostaticchuck used to develop a reticle-clamping force when energized orelectrically charged, and to release the reticle when de-energized,shorted or otherwise electrically discharged.

An exemplary method for transitioning a substrate from atmosphericpressure to vacuum in a lithography tool using a substrate transportsystem in accordance with an embodiment of the present invention willnow be described with reference to FIGS. 9A-9K.

In FIG. 9A, atmospheric robot 901 is shown placingbox-cassette-substrate arrangement (box 903 containing removablesubstrate transport cassette 800 and substrate 801) on a shelf 909 infirst storage rack 911. Upon request for a specific reticle, atmosphericrobot 901 transfers the box-cassette-substrate arrangement from rack 911to entry-exit module 913 shown in FIG. 9B.

Referring to FIG. 9B, box lid 915 rests on ledge 917 of the module 913.A detacher (not shown) unlatches box lid 915 from base 919. Base 919rests on elevator 921.

Next, as shown in FIG. 9C, elevator 921 lowers base 919, which supportsthe cassette-substrate arrangement (removable substrate transportcassette 800 containing substrate 801) away from lid 915. Shuttle 923remains parked inside loadlock 925, thus allowing elevator 921, base 919and the cassette-substrate arrangement to move down past shuttle 923without colliding.

Referring to FIGS. 9D and 9E, shuttle 923 moves to thecassette-substrate arrangement and grabs it. Then elevator 921 furtherlowers base 919 so that the shuttle 923 can move past base locators 929.At this point, the base portion 807 of the cassette-substratearrangement rests solely on shuttle fingers 927. Shuttle 923 then movesthe cassette-substrate arrangement into loadlock 925.

Turning to FIGS. 9F and 9G, with shuttle 923 still inside loadlock 925,elevator 921 raises base 919 up to lid 915. The box latching/unlatchingdevice (not shown), latches the base 919 and the lid 915 together. Atthis point, elevator 921 moves down, leaving box 903 resting on ledge917.

If desired, the atmospheric robot 901 can now remove the empty box 903and replace it with another box-cassette-substrate arrangement. Forexample, in a lithography tool having two entry-exit modules 913, afirst module 913 can be dedicated to performing the substrate inputfunction and a second module 913 can be dedicated to performing thesubstrate output function. In that case, the atmospheric robot 901 wouldremove empty boxes 903 from the first module 913 and place them in thesecond module 913 for accepting already processed reticles. Theatmospheric robot 901 would then remove the box 903 containing theprocessed substrate from the second module 913 and place it in thestorage rack. Next, the atmospheric robot 901 would take the box 903containing the next substrate to be processed from the storage rack andplace it in the first module 913. On the other hand, in a lithographytool having only one entry-exit module 913, the module 913 would be usedfor both input and output of reticles. In this case, it is likely thatthe atmospheric robot 901 would wait until the reticle has beenprocessed and is back inside its box 903 before removing the box 903.Other sequences that maximize production throughput for tools having asingle or multiple entry-exit modules 913 will be apparent to thoseskilled in the relevant arts based on the disclosures herein. Thesesequences may or may not require removal of empty boxes 903 fromentry-exit modules 913 for maximizing throughput.

With elevator 921 out of its way, as shown in FIG. 9G, shuttle 923retracts over the elevator 921 clearing the way for atmospheric-sidegate valve 931 to close. Loadlock 925 is then pumped down. As explainedabove, box 903 may or may not be present at this point.

Referring to FIG. 9H, once the desired vacuum level has been achievedinside loadlock 925, vacuum-side gate valve 933 opens, vacuum robot 935reaches into loadlock 925 and picks up the cassette-substratearrangement, bringing it inside process chamber 937.

Turning to FIG. 91, vacuum robot 935 next transfers thecassette-substrate arrangement to second storage rack 939 within processchamber 937. FIG. 91 shows a simplified front view of the second storagerack 939, having shelves 941 and ledges 943. In this view, the directionof insertion and removal of reticles is perpendicular to the page.Referring to the lower half of FIG. 91, the end effector 940 of vacuumrobot 935 is shown inserting the cassette-substrate arrangement ontobottom shelf 941. In an embodiment, the insertion takes place at a levelhigh enough to avoid interference of edge band 821 of top 811 withledges 943. After performing the horizontal insertion motion, using endeffector 940, vacuum robot 935 lowers the bottom portion 807 onto bottomshelf 941 and withdraws.

Referring to the upper half of FIG. 91, bottom portion 807 is shownresting on middle shelf 941 after being placed there by the vacuum robot935. During said downward robot motion, surface 825 of edge band 821comes to rest on ledges 943, thus causing top portion 811 to separatefrom baseplate 807, which continues on downward until reaching shelf941. Thus, in an embodiment, all the cassette-substrate arrangements arestored in the second storage rack in an open condition. After insertingits end effector portion between shelf 941 and baseplate 807, vacuumrobot 935 can extract bottom portion 807 and substrate 801 for mountingsubstrate 801 onto the stage by performing a short upward motion. Thismotion provides for the removal of the bottom portion 807 and substrate801, but not top portion 811. Further details of this process will bedescribed below. After the short upward motion, substrate 801 does notcontact top portion 811, which is still supported by ledges 943. Next,vacuum robot 935 extracts base portion 807 and substrate 801 using ahorizontal motion perpendicular to the page, leaving top portion 811resting on ledges 943. For ejecting a substrate from the litho tool,vacuum robot 935 removes the entire cassette-substrate arrangement byfollowing the insertion motion sequence in exact reverse order, asexplained above and as illustrated in the bottom half of FIG. 91.Further steps for processing the substrate in a lithographic exposurestage of the process chamber 937 will now be described with reference toFIGS. 9J and 9K.

In preparation for lithographic exposure, vacuum robot 935 placessubstrate 801 onto chuck 945 of lithographic exposure stage 947. Vacuumrobot 935 first moves upwards until substrate 801 contacts chuck 945.Next, chuck 945 is energized, thereby clamping the substrate 801. (FIG.9J) Afterwards, the vacuum robot 935 moves downward, leaving substrate801 attached to the chuck 945 but carrying away base portion 807 whichis not attracted to the chuck 945. (FIG. 9K) Release and removal of thesubstrate from the exposure stage 947 follows the sequence in exactreverse order.

Programmed computer systems are used to execute programs directing themanipulation of substrates, components, and other features oflithography systems. Based on the teachings described herein, the designof programs for implementing the systems and methods of the presentinvention will be apparent to persons skilled in the relevant arts.

CONCLUSION

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be understood by those skilledin the art that various changes in form and details can be made hereinwithout departing from the spirit and scope of the invention, as definedin the appended claims. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections can set forth one or more,but not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

1. A substrate transport system for transitioning a substrate fromatmospheric pressure to vacuum in a lithography tool, comprising: one ormore removable substrate transport cassettes, each removable substratetransport cassette having at least one vent and at least one filter, andeach removable substrate transport cassette supporting one substrateforming a cassette-substrate arrangement; a box having a base and a lid,wherein said box holds one or more of said cassette-substratearrangements, forming a box-cassette-substrate arrangement; a firststorage rack having one or more shelves for holding saidbox-cassette-substrate arrangement; and an entry-exit module having aloadlock that transitions said cassette-substrate arrangement fromatmospheric pressure to vacuum, said at least one vent and said at leastone filter restricting particles within said loadlock from entering saidcassette-substrate arrangement and reaching a surface of the substrate.2. The substrate transport system of claim 1, wherein said entry-exitmodule further comprises an atmospheric de-podder.
 3. The substratetransport system of claim 1, wherein said entry-exit module furthercomprises an elevator that raises and lowers said cassette-substratearrangement.
 4. The substrate transport system of claim 1, wherein saidentry-exit module further comprises a shuttle that engages saidcassette-substrate arrangement and transports said cassette-substratearrangement into said loadlock.
 5. The substrate transport system ofclaim 1, further comprising a process chamber that receives saidcassette-substrate arrangement after said cassette-substrate arrangementhas been transitioned to vacuum.
 6. The substrate transport system ofclaim 5, further comprising a second storage rack within said processchamber, said second storage rack having a plurality of shelves to storesaid cassette-substrate arrangement.
 7. A method for transitioning asubstrate from atmospheric pressure to vacuum in a lithography tool,comprising: (a) loading the substrate into a removable substratetransport cassette to produce a cassette-substrate arrangement, whereinsaid removable substrate transport cassette has at least one vent and atleast one filter; (b) loading said cassette-substrate arrangement into abox to produce a box-cassette-substrate arrangement, said box comprisedof a base and a lid; (c) transporting said box-cassette-substratearrangement to a shelf of a first storage rack; (d) transporting saidbox-cassette-substrate arrangement out of vacuum from said first storagerack to an entry-exit module; (e) unlatching a lid of said box from abase of said box; (f) lowering said base on an elevator, said basesupporting said cassette-substrate arrangement; (g) engaging saidcassette-substrate arrangement with a shuttle; (h) using said shuttle totransport said cassette-substrate arrangement into a loadlock; and (i)transitioning said loadlock from atmospheric pressure to vacuum, whereinduring transitioning, said at least one vent and said at least onefilter restrict particles within said loadlock from entering saidcassette-substrate arrangement and reaching a surface of the substrate.8. The method of claim 7, further comprising transporting saidcassette-substrate arrangement from said loadlock to a process chamberafter completing said transitioning step (i).
 9. The method of claim 8,further comprising storing said cassette-substrate arrangement on ashelf in a second storage rack located within said process chamber. 10.The method of claim 9, wherein said storing step comprises insertingsaid cassette-substrate arrangement so that an edge band of saidremovable substrate transport cassette is above a set of ledgesassociated with a shelf of an in-vacuum library.
 11. The method of claim10, further comprising lowering said removable substrate transportcassette so that a base portion of said removable substrate transportcassette rests on a bottom surface of said shelf and a top portion ofsaid removable substrate transport cassette rests on said set of ledgesassociated with said shelf.
 12. The substrate transport system of claim1, wherein each removable substrate transport cassette comprises: a baseportion and a top portion; one or more base portion locators disposedwithin said base portion that supports one or more lower corners of thesubstrate; and one or more upper portion locators disposed within saidtop portion in which one or more upper corners of the substrate arefitted, wherein said at least one filter and said at least one vent arelocated opposite a patterned side of said substrate.
 13. The substratetransport system of claim 12, wherein each removable substrate transportcassette further comprises a seal that seals said base portion and saidtop portion after the substrate has been positioned within the removablesubstrate transport cassette.
 14. The substrate transport system ofclaim 13, wherein said seal is permeable to gases but substantiallyimpermeable to particles.
 15. The substrate transport system of claim13, wherein said seal is comprised of a raised surface with protrudingconcentric vertical flanges that fit into one or more correspondinggrooves on said top portion.
 16. The substrate transport system of claim13, wherein said seal is impermeable to gases and substantiallyimpermeable to particles.
 17. The substrate transport system of claim13, wherein said seal is an O-ring elastomer seal.
 18. The substratetransport system of claim 12, wherein each removable substrate transportcassette further comprises an edge band surrounding one or more sideedges of said base portion, wherein said edge band impedes the migrationof particles from outside the removable substrate transport cassette toinside and further wherein said edge band provides a surface to supportsaid top portion.